Nitrifying biomass characterization and monitoring during bioaugmentation in a membrane bioreactor

Nitrification performance and bacterial community dynamics in a membrane bioreactor with elevated ammonia concentration: The combined inhibition effect of salinity, free ammonia and free nitrous acid on nitrification at high ammonia loading rates

The responses of the operational performance and bacterial community structure of a nitrification membrane bioreactor (MBR) to elevated ammonia loading rate (ALR) were investigated. Effective nitrification performance was achieved at high ALR up to 3.43 kg NH₄⁺-N/m³·d, corresponding to influent NH₄⁺-N concentration of 2000 mg/L. Further increasing influent NH₄⁺-N concentration to 3000 mg/L, the MBR system finally became completely inefficient due to the combined inhibition effect of salinity, free ammonia and free nitrous acid on nitrification. Ammonia-oxidizing bacteria (AOB) Nitrosomonas were enriched with the increase of ALR. The relative abundance of Nitrosomonas in the sludge with ALR of 2.57 kg NH₄⁺-N/m³·d was up to 14.82%, which were 9-fold and 53-fold higher than that in seed sludge and the sludge with ALR of 0.10 kg NH₄⁺-N/m³·d, respectively. The phylogenetic analysis of AOB amoA genes showed that Nitrosomonas europaea/mobilis lineage are chiefly responsible for catalyzing ammonia oxidation at high ALRs.

Kinetics of aerobic granular sludge treating low-strength synthetic wastewater at high dissolved oxygen

Three parallel reactors (i.e. R1-R3) were operated with 340 mg-COD L^-1, 42 mg-TN L^-1, and 7 mg-TP L^-1 at 20 ± 1°C. A mature granular sludge developed in 40 d and was stable for the 120 d experimentation period at an average food to microorganism ratio of 0.25 ± 0.08 g-COD g-VSS^-1 d^-1. Reactor biomass had higher inorganic content (i.e. 0.78-0.80 g-VSS g-TSS^-1) than effluent biomass (i.e. 0.88-0.92 g-VSS g-TSS^-1). Average granule diameter was 0.7-1.0 mm. Maximum phosphorus uptake and release rates averaged 4 ± 3 and 4 ± 2 mg-P g-VSS^-1 h^-1, respectively. Maximum observed nitrification rates averaged 1.9 ± 0.6 mg-N g-VSS^-1 h^-1. Phosphorus kinetics were similar between R1-R3 (i.e. P = 0.5309-0.6870) while nitrification kinetics varied significantly (i.e. P = 0.0002) even though conditions were the same. Effluent phosphate was on average 0.2 ± 0.4 mg-P L^-1 while total inorganic nitrogen removal averaged 60 ± 10% resulting in an average effluent of 17 mg-N L^-1. Aerobic granular sludge was capable of reliable nutrient removal from low-strength wastewater without volatile fatty acid source and at high dissolved oxygen concentrations.

From the Inside Out: an Epibiotic Bdellovibrio Predator with an Expanded Genomic Complement

Bdellovibrio and like organisms are abundant environmental parasitoids of prokaryotes that show diverse predation strategies. The vast majority of studied Bdellovibrio bacteria and like organisms deploy intraperiplasmic replication inside the prey cell, while few isolates with smaller genomes consume their prey from the outside in an epibiotic manner. The novel parasitoid "Candidatus Bdellovibrio qaytius" was isolated from a eutrophic freshwater pond in British Columbia, where it was a continual part of the microbial community. "Ca Bdellovibrio qaytius" was found to preferentially prey on the betaproteobacterium Paraburkholderia fungorum without entering the periplasm. Despite its epibiotic replication strategy, "Ca Bdellovibrio" encodes a large genomic complement more similar to that of complex periplasmic predators. Functional genomic annotation further revealed several biosynthesis pathways not previously found in epibiotic predators, indicating that "Ca Bdellovibrio" represents an intermediate phenotype and at the same time narrowing down the genomic complement specific to epibiotic predators. In phylogenetic analysis, "Ca Bdellovibrio qaytius" occupies a widely distributed, but poorly characterized, basal cluster within the genus Bdellovibrio This suggests that epibiotic predation might be a common predation type in nature and that epibiotic predation could be the ancestral predation type in the genus.IMPORTANCE Bdellovibrio and like organisms are bacteria that prey on other bacteria and are widespread in the environment. Most of the known Bdellovibrio species enter the space between the inner and outer prey membrane, where they consume their prey cells. However, one Bdellovibrio species has been described that consumes its prey from the outside. Here, we describe "Ca Bdellovibrio qaytius," a novel member of the genus Bdellovibrio that also remains outside the prey cell throughout its replication cycle. Unexpectedly, the genome of "Ca Bdellovibrio" is much more similar to the genomes of intracellular predators than to the species with a similar life cycle. Since "Ca Bdellovibrio" is also a basal representative of this genus, we hypothesize that extracellular predation could be the ancestral predation strategy.

Low temperature effects on nitrification and nitrifier community structure in V-ASP for decentralized wastewater treatment and its improvement by bio-augmentation

The vegetation-activated sludge process (V-ASP) has been proved to be an environment-friendly decentralized wastewater treatment system with extra esthetic function and less footprint. However, the effects of low temperature on the treatment performance of V-ASP and related improvement methods are rarely investigated, up to now. In this work, the effect of low temperature on nitrification in V-ASP was comprehensively investigated from overall nitrification performance, substrate utilization kinetics, functional enzymatic activities, and microbial community structure shift by comparison with conventional ASP. Bio-augmentation methods in terms of single-time nitrifier-enriched biomass dosage were employed to improve nitrification efficiency in bench- and full-scale systems. The experiment results demonstrated that the NH₄⁺-N removal efficiency in V-ASP system decreased when the operational temperature decreased from 30 to 15 °C, and the decreasing extent was rather smaller compared to ASP, as well as ammonium and nitrite oxidation rates and enzymatic activities, which indicated the V-ASP system possesses high resistance to low temperature. With direct dosage of 1.6 mg nitrifier/gSS sludge, the nitrification efficiency in V-ASP was enhanced dramatically from below 50% to above 90%, implying that bio-augmentation was effective for V-ASP whose enzymatic activities and microbial communities were both also improved. The feasibility and effectiveness of bio-augmentation was further confirmed in a full-scale V-ASP system after a long-term experiment which is instructive for the practical application.

Enrichment and application of nitrifying activated sludge in membrane bioreactors

In this study, nitrifying bacteria were enriched in a membrane bioreactor (MBR, R1) and their bioaugmentation effectiveness was evaluated in another two MBRs (R2 and R3). Nitrifying activated sludge (NAS) with high nitrification activity of up to 3,000 mg-N/(L·d)^-1 was successfully enriched in R1. The results showed that chemical oxygen demand concentration of 100-200 mg/L had no negative effect on NAS enrichment but reduced the ratio of bacterial nitrifiers. Moreover, the cell concentration of nitrifying bacteria in NAS, which was 3.1 × 10¹¹ cells/L, was similar to that of the commercial bacterium agent. For the bioaugmentation test, the reactor inoculated with 14% NAS achieved a 23% higher NH₄⁺-N removal efficiency than that of the uninoculated reactor. Along with the improvement of nitrification performance, the bacterial nitrifiers abundance and microbial richness remarkably increased after bioaugmentation. These results suggested that the MBR system could efficiently enrich nitrifying bacteria using organic carbon containing culture medium, and potentially act as a side-stream reactor to enhance the nitrification function of the wastewater treatment plant.